ReactiveCocoa: Subscribe only to new values

Question

I've created an event subscriber in viewDidLoad, as follows:

[RACObserve(_authenticationView.passwordInput.textField, text) subscribeNext:^(NSString* text)
{
     //handle this
}];

This fires whenever the textField.text property changes (expected), however it also fires once when created, or for the intitial value, which is not what I want.

Of course I could filter this out, but I only want to filter the first event out. How do I do this?

Requirements:

• If the password has a new empty value, present a validation message (can't proceed password empty).
• If the password has a new non-empty value, talk to remote client.

. . so what's the cleanest way to do this?

Answer 1

You can use different approaches:

1. -skip:1 to skip first value.

[[RACObserve(_authenticationView.passwordInput.textField, text) skip:1] subscribeNext:^(NSString* text) {
    //handle this
}];

---

2. -ignore:nil to skip initial nil value.

[[RACObserve(_authenticationView.passwordInput.textField, text) ignore:nil] subscribeNext:^(NSString* text) {
    //handle this
}];

---

3. -distinctUntilChanged to skip new values, that equal previous.

[[RACObserve(_authenticationView.passwordInput.textField, text) distinctUntilChanged] subscribeNext:^(NSString* text) {
    //handle this
}];